The present invention relates to a novel and improved screw extruder for molding plastics material, and more particularly to a movable extruder having an extruding means mounted on a column standing on a pedestal.
An extruder of type employing a column needs to be stable free from troubles such as turning over during the operation and transportation thereof, even when the extruding means is located at a high position on the column, and therefore must fulfill the essential requirements that the extruding means is to be compact, light in weight and well-balanced. Further, to readily remove the screw from the screw unit in order to clean the inside thereof is another essential requirement in addition to those in economy, operability and the above-mentioned stability.
Conventional movable extruders generally provided with multiple stage ordinary reduction gear are expensive, large in volume and heavy in weight, since it needs from two to four reduction stages to get a suitable screw speed through the speed of the prime mover owing to comparatively small reduction ratio per one stage, which results from the fact that the arrangement and dimensions of parts contained therein are so restricted that the peripheries thereof should be surely aparted from the shaft supporting the screw and/or should not invade the cylindrical space behind the screw so as to form a shaft formed with a piercing hole into which a bar for removing the screw is insertionable from the backside of the gear box. Consequently, in the extruder employing such a multiple stage reduction gear, the bending moment applied to the column becomes remarkably large and therefore the stability thereof is aggravated, since the weight per power capacity is relatively heavy and the extruding means is to be sufficiently aparted from the column owing to the necessary large volume around the screw.
The worm gear has been often employed in the extruder instead of the multiple stage ordinary reduction gear. While a comparatively large reduction ratio is obtainable by a single stage worm gear, there are many troublesome deficiencies such as a tendency that the lubricant becomes overheated, a heavy weight, largeness in volume and short durability due to the abrasion of teeth caused by the friction cntact therebetween.
On the other hand, although the planetary gear is superior to the above-mentioned gears in viewpoint of the efficiency of power transmission, the compactness and lightness in weight, as well as silencity and less vibration and therefore is quite suitable for the extruder, especially for the movable extruder which is not fixed on a ground, it is difficult to install a device for removing the screw from the screw unit in order to clean the inside thereof, since it has generally an output and input shaft in axially aligned and the input shaft impedes to touch directly the end of the screw supported in the screw sleeve from the backside of the reduction unit. Therefore, the coventional extruder of column type has not adopted the planetary gear.
The conventional extruder has often utilized the extruding means which is devided into a screw unit not provided with a speed reduction means and a power source which includes a speed reduction gear and motor, or gearmotor. In that case, the extruder is apt to become out-of-balance since the weight of the power source is rather heavier than that of the screw unit, which is aggravated in accordance with the tendency in recent years employing a motor of larger power. Additionally, as for the device which transmits power from the power source to the screw unit, chain transmission should be employed, since the output shaft of the power source is rotated by large torque and low speed and the center distance is rather long. However, the chain transmission is not suitable for the extruder of column type in viewpoint of large noise and short durability when operated without lubricant.
The screw extruder of the invention having a well-balanced extruding means consisting of a extruding unit provided with a reduction gear and a prime mover is capable of employing a belt transmission and is therefore quite stable and silent during the operation.
In an extruder for molding plastics material, to readily remove the screw from the screw unit in order to clean the inside thereof is another essential requirement. The conventional extruder has often employed the mechanism therefor comprising a cap nut which is threaded onto the end of the screw sleeve supporting the screw and is formed with a threaded hole at the center portion thereof and a threaded bar which has an enough length to push the end of the screw and is threaded into the hole of the cap nut. In the conventional extruder employing the multiple stage ordinary reduction gear, although there are some aforesaid deficiencies, it is rather easy to equip with such mechanism owing to the comparative free arrangement of parts contained therein.
As for the extruder employing the planetary gear having an output shaft and input shaft aligned in a line, it is quite difficult to apply such mechanism, as mentioned above, and therefore the planetary gear has never been employed. The screw extruder of the invention can dissolve the difficulty by forming a piercing hole extending through the input shaft and output shaft. In other words, it can say that the extruder of the invention is accomplished as a result of conversion from this demerit into a merit.
A further problem concerning oil leakage from an oil room into the piercing hole in the shaft arises in case of the extruder equipped with a planetary gear. In the extruder employing the multiple stage ordinary reduction gear having a wide range of shaft arrangement, it is rather easy to devise a countermove against this oil leakage by separating the output shaft from the input shaft and by forming the output shaft, i.e. screw sleeve formed with a piercing hole therethrough extending until the backside of the gear box.
However, as for the extruder equipped with a reduction gear having an output shaft and input shaft aligned in a line, for instance, planetary gear, it is necessary to consider a satisfactory counterplan in order to preclude leaks from the oil room into the piercing hole communicating with the oil room at the gap between the opposing ends of input shaft and output shaft which are, of course, longitudinally to be separated each other due to the difference in speed.
The extruder of the invention employs a sealing mechanism consisting of a boss extending from the end of the output shaft and being inserted in the hole formed in the opposing end of the input shaft and an oil seal positioned between the boss and the opposing hole, or a boss extending from the end of the input shaft and being inserted in the hole formed in the opposing end of the output shaft and the oil seal.